Essential fatty acid metabolism in cultured human airway epithelial cells.

To characterize essential fatty acid metabolism of human airway epithelium, we examined the capacity of epithelial cells to incorporate and desaturate/elongate 18:2(n - 6) and the turnover of phospholipid fatty acyl chains in these cells. Epithelial cells were cultured for 5-7 days and incubated with [1-14C]18:2(n - 6) (1 microCi, 100 nmol). The essential fatty acid profile of the cells was readily modified by 18:2(n - 6) supplementation to culture medium. After 4 h incubation, 32 +/- 5.6 nmol of [1-14C]18:2(n - 6) was incorporated into phospholipids (65 +/- 9.5%, of which 74% was incorporated into phosphatidylcholine (PC)) and neutral lipid (31 +/- 10%) per mg protein of cultured cells. 30 +/- 8% of [1-14C]18:2(n - 6) incorporated, was converted to homologous trienes, tetraenes and pentaenes, the major products being 20:3(n - 6) and 20:4(n - 6). The conversion of 18:2(n - 6) was time-dependent and donor age-related. A higher proportion of 20:3(n - 6) and 20:4(n - 6) was incorporated into phosphatidylinositol (PI) and phosphatidylethanolamine (PE). About 10-15% of total products formed from 18:2(n - 6) was released from membrane to culture medium. Both 20:4(n - 6) and 20:5(n - 3) inhibited 18:2(n - 6) incorporation and desaturation. Rate of incorporation of 18:2(n - 6) was more than either 18:1(n - 9) or 16:0. With pulse-chase studies, the half-life of 18:2(n - 6) in PC, PI and PE was estimated to be 5.5, 6.0 and 7.3 h, respectively. These data indicate active metabolism of essential fatty acids in human airway epithelial cells. This metabolism may play a key role in the regulation of membrane properties and function in these cells.

The chloride channel blocker anthracene 9-carboxylate inhibits fatty acid incorporation into phospholipid in cultured human airway epithelial cells.

This study investigated whether making epithelial cell membranes impermeable to Cl- movement affects incorporation of fatty acids into membrane constituents. Epithelial cells were isolated from human nasal polyps, cultured for 5-7 days, and used to test the effect of anthracene 9-carboxylate (9-AC), known to inhibit Cl- conductance across the epithelial membrane, on the incorporation and desaturation of [1-14C]linoleic acid (C18:2,n-6) in experiments of up to 4 h duration. 9-AC (5 mM) reduced C18:2,n-6 incorporation into phospholipid by 60-70%, and increased incorporation of C18:2,n-6 into triacylglycerol by 50-100%. The decrease in C18:2,n-6 incorporation into phospholipid was rapid and dependent on the concentration of 9-AC. Substitution of extracellular Cl- with gluconate significantly decreased C18:2,n-6 incorporation into phospholipid, suggesting that the effect of 9-AC may occur by inhibiting Cl- conductance. Lipid analysis of cells exposed to 50 microM-C18:2 revealed that, as a consequence of the effect of 9-AC, the level of C18:2,n-6 in cell membrane phospholipid was significantly lowered. The relative rate of C18:2,n-6 desaturation was not apparently changed by 9-AC. These data suggest that Cl- conductance may play a role in fatty acid incorporation into epithelial cell membrane phospholipids.